We are understanding how general anesthetics interact with proteins. A fluorescence quenching method has been developed to examine this question. The volatile general anesthetic halothane is equilibrated with buffer and added at predetermined dilutions to a protein solution and the native tryptophan fluorescence quenching is measured. ree L-tryptophan fluorescence in methanol can be quenched by halothane at much higher concentrations of solvent phase anesthetic. The fluorescence quenching is collisional in nature and is probably caused by the bromine atom on the anesthetic. The interpretation of the protein data is that halothane partitions into hydrophobic domains in the vicinity of the indole rings. The question we are answering is whether this is a static (implying specific binding to the protein) or collisional quenching process for the halothane-protein interaction. Time resolved fluorescence lifetime measurements are allowing static and collisional quenching to be distinguished.